1. Field of the Invention
The present invention relates to a face authentication system and a face authentication method for performing a registration process and a verification process of authentication data, and the like, based on three-dimensional data relating to a face area of a human.
2. Description of Related Art
Heretofore, there have been proposed various biometrics methods, using two-dimensional image data concerning a face area of a human. For instance, there is known a method comprising: pre-registering image information after acquiring a two-dimensional image including a face area of a person (hereinafter, also called as “subject”) whose authentication is required, and specifying the face area by matching the acquired two-dimensional image with a predetermined face template; and comparing an image relating to the face area acquired in authentication with the registered image in feature quantity.
Japanese Unexamined Patent Publication No. 2004-126738 proposes a biometrics method for performing personal authentication, with use of a three-dimensional shape measuring apparatus for acquiring three-dimensional data concerning a face area of a subject, in addition to an image sensing apparatus for acquiring two-dimensional image data, by referring to the acquired two-dimensional image data and three-dimensional data. With use of the method, an authentication process can be performed, with the three-dimensional feature quantity relating to the face area being included, whereby more accurate and efficient authentication is executable. Japanese Unexamined Patent Publication No. 2000-76460 discloses a technique of displaying a three-dimensional data missing area on a two-dimensional image, in acquiring two-dimensional image data and three-dimensional data concerning a subject.
It is highly likely that a part of three-dimensional data may be missing depending on a face orientation of a subject or a like factor in acquiring the three-dimensional data relating to a face area of the subject. Three-dimensional data is measured by e.g. a method of projecting pattern light onto a subject and receiving light reflected on the subject. If the face of the subject does not face forward with respect to an imaging optical system of the image sensing apparatus, the three-dimensional shape measuring apparatus fails to receive a sufficient amount of light reflected on a sharply inclined part of the face area e.g. a cheek or its vicinity. In such a case, the image area having the insufficient light receiving amount may result in a data missing part.
If the template of the subject is registered in a state that the data missing part is included, the authentication precision may be lowered. In view of this, it is desirable to rate the quality of three-dimensional data acquired in the registration. The same idea is also applied to three-dimensional data to be acquired in the verification. Simply calculating a ratio of the three-dimensional data missing part relative to the face area is insufficient to rate the quality of the three-dimensional data. This is because, by the simple calculation of the ratio of the three-dimensional data missing part, it is difficult or impossible to determine whether the data is missing due to an improper face orientation or the like, or based on an improper photographing condition or a like condition e.g. a poor illumination condition or existence of an obstacle which may block the subject in image shooting.